Polycystic kidney disease (PKD) is one of a group of ciliopathies characterized by the growth of fluid filled cysts in several organs, predominately in kidney tubules and liver bile ducts. This group of genetic diseases, that also includes Bardt Biedl syndrome, Meckel Gruber syndrome, nephronophthisis, and oral-facial-digital syndrome, have been linked by the findings that the mutated genes encode proteins located in the primary cilium of the epithelial cells that line the normal tubule or duct and ultimately line the cysts that form in these tissues. The genes encode proteins of a transient receptor potential Ca2+ channel. While the proteins linked to the various ciliopathies are found in other subcellular structures including the tight junctions, the finding of commonality in the primary cilium combined with the postulated function of this structure as an osmotic or flow censor, has lead to the postulate that aberrant ciliary function underlies cyst formation and growth.
Growth of cysts may occur in various cystic diseases such as polycystic kidney disease (PKD), polycystic liver disease (PLD), Bardt Biedl syndrome, nephronophthisis, Meckel Gruber syndrome and oral-facial-digital syndrome. Additionally, aberrant cyst growth may occur that is not associated with these diseases. Without being bound by theory, it is believed herein that cyst expansion may be a function of the stimulation of ion secretory events that cause increased movement of electrolytes and, secondarily, water into the cyst lumen. It has been shown that in PKD renal tissue, those events may be caused by agents that increase intracellular cAMP which, in turn, stimulate ion channels in the apical plasma membrane (Ye & Grantham, N Engl J Med, 329:310-313 (1993); Grantham et al., J Clin Invest 95:195-202 (1995); Mangoo-Karim et al., Am J Physiol 269:F381-388 (1995); Davidow et al., Kidney Int 50:208-218 (1996). These observations have been extended to liver cysts formed from the cholangiocytes which line the liver bile ducts (Muchatuta et al., Exper Biol Med 234:17-27 (2009). In agreement with this contention are studies done first in rodent models of PKD and currently in clinical trials, showing that for example antagonists of the vasopressin V2 receptor in renal cells inhibit cAMP formation and cyst growth (Gattone et al. Nat Med 9:1323-1336 (2003).
Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the slow growth of multiple fluid-filled cysts in the kidney and liver. The factors involved in cyst growth or changes in the rate of cyst growth are unknown. However, previous studies have demonstrated that renal injury results in exacerbation of cyst growth. Cyst growth in autosomal dominant polycystic kidney disease (ADPKD) is a slow process that may proceed over decades. Despite the formation of multiple, large cysts during ageing, renal function is usually not severely compromised until the fifth decade of life but then declines rather precipitously. Renal injury or tubular cell damage exacerbates cyst formation and expansion.
Cyst growth is thought to result from stimulation of ion secretory events that cause increased movement of electrolytes and, secondarily, water into the cyst lumen resulting in cyst expansion. It has been observed that increased intracellular cAMP in PKD renal tissue stimulates ion channels, predominately the cystic fibrosis transmembrane conductance regulator (CFTR) in the apical membrane, and also in the cholangiocytes that line liver bile ducts. Similarly, in rodent models of PKD and currently in clinical trials, it has been shown that antagonists of the vasopressin V2 receptor in renal cells or somatostatin agonists in cholangiocytes and renal tissue inhibit both cAMP formation and cyst growth.
However, pharmaceutical agents in clinical trials are reported interfere with the action of hormones that increase cAMP in target cells. In the kidney, antidiuretic hormone (ADH; vasopressin) regulates salt and water balance via a signaling pathway that increases intracellular cAMP. In the bile ducts, somatostatin, via a separate hormone receptor, decreases intracellular cAMP. In addition to mediating hormone action, cAMP also causes an increase in activity of the CFTR (cystic fibrosis transmembrane regulator) channel that transports Cl− into the cysts with the consequent movement of fluid and cyst expansion.
Thus, agents that decrease cAMP, such as vasopressin receptor antagonists, such as in the kidney, or somatostatin receptor agonists, such as in hepatic bile ducts, have been the subject of investigation for decreasing cyst growth. However, those agents may have limited utility because they are organ specific. Further, those agents may be prone to the side effects because they will likely also interfere with natural hormone signaling. Thus, there is yet a need for pharmaceutical agents capable of targeting the organ systems that are affected by cystic diseases such as PKD, PLD, Bardt Biedl syndrome, nephronophthisis. Meckel Gruber syndrome and oral-facial-digital syndrome, as well as other cystic formations not associated with these diseases.
It has been discovered herein that treatment with LPA antagonists that block the ability of LPA to interact with its receptor may inhibit electrolyte and fluid secretion and thereby block cyst initiation and/or growth. Thus, these agents are useful in preventing cyst formation and/or expansion in the kidney and hepatic bile ducts as well as in any other organs that are normally lined with polarized epithelial cells and show cyst formation during disease progression, such as the pancreas. Therefore, LPA antagonists are useful in the treatment of and/or prevention of cysts.
Using the mpkCCDcl4 cell line model of renal principal cells, it has been discovered herein that LPA (lysophosphatic acid), a component of cyst fluid, is a factor that stimulates secretory Cl− transport via at least two anion channels. The LPA effect is manifested via receptors located on the basolateral membrane of the polarized renal principal cells and stimulates channel activity in the apical membrane. The concentrations of LPA measured in human cyst fluid and serum are sufficient to maximally stimulate ion transport. Without out being bound by theory, it is believed herein that renal injury and subsequent blood or cyst fluid seepage into the interstitial space is capable of providing a secretory stimulus to remaining, intact cysts resulting on overall cyst growth.
Further, cyst fluid obtained from human patients can stimulate secretory activity when added to renal epithelial cells. It has been reported that lipid-like component(s) of the cyst fluid could stimulate this Cl− secretory activity in both Madin Darby Canine Kidney (MDCK) cells and in primary cultures of ADPKD cells, and it has been suggested that the major active component in the cyst fluid is an endogenous forskolin.
In order to fully characterize the Cl− secretory response, electrophysiological techniques have been used herein to examine the effect of cyst fluid when added to a murine cell culture model of the principal cells, the mpkCCDcl4 (mouse principal cells of the kidney cortical collecting duct, clone 4). In this model, human renal cyst fluid stimulates at least two different Cl− channels.
It has been discovered herein that the active component of the cyst fluid used in these studies is lysophosphatic acid (LPA) present in the cyst fluid in a concentration that maximally stimulates ion transport. In addition, it has been discovered herein that LPA concentrations in normal serum are also capable of maximally stimulating the Cl− transporters. Under normal conditions, the LPA is bound to proteins in the cyst fluid or bloodstream and, therefore, unavailable for binding to the LPA receptors on the basolateral membrane of the epithelial cells lining the cysts. Under conditions such as injury or loss of cyst wall integrity due to aging and/or cyst size, the LPA-protein complexes would be released into the interstitial space where they interact with specific receptors to exacerbate cyst growth.
It has also been discovered herein that treatment with inhibitors of TMEM16a may inhibit electrolyte and fluid secretion and thereby block cyst initiation and/or growth. Thus, these agents are useful in preventing cyst formation and/or expansion in the kidney and hepatic bile ducts as well as in any other organs, such as the pancreas. Therefore, TMEM16a inhibitors are useful in the treatment and/or prevention of cysts.
It has also been discovered herein that treatment with peroxisome proliferator-activated receptor (PPAR) modulators, such as PPAR gamma modulators may inhibit electrolyte and fluid secretion and thereby block cyst initiation and/or growth. Thus, these agents are useful in preventing cyst formation and/or expansion in the kidney and hepatic bile ducts as well as in any other organs, such as the pancreas. Therefore. PPAR gamma modulators are useful in the treatment and/or prevention of cysts.
In one embodiment, described herein are methods for treating cystic diseases in a patient, where the methods include the step of administering a therapeutically effective amount of one or more LPA receptor antagonists. In another embodiment, described herein are methods for treating cystic diseases in a patient, where the methods include the step of administering a therapeutically effective amount of one or more TMEM16a inhibitors. In another embodiment, described herein are methods for treating cystic diseases in a patient, where the methods include the step of administering a therapeutically effective amount of one or more PPAR gamma modulators.
In another embodiment, described herein are methods for treating cystic diseases in a patient, where the methods include the step of administering a therapeutically effective amount of one or more LPA receptor antagonists and one or more TMEM16a inhibitors. In another embodiment, described herein are methods for treating cystic diseases in a patient, where the methods include the step of administering a therapeutically effective amount of one or more LPA receptor antagonists and one or more PPAR gamma modulators. In another embodiment, described herein are methods for treating cystic diseases in a patient, where the methods include the step of administering a therapeutically effective amount of one or more TMEM16a inhibitors and one or more PPAR gamma modulators. In another embodiment, described herein are methods for treating cystic diseases in a patient, where the methods include the step of administering a therapeutically effective amount of one or more LPA receptor antagonists, one or more TMEM16a inhibitors, and one or more PPAR gamma modulators.
In another embodiment, described herein are methods for reducing electrolyte and fluid secretion in a patient having or suspected of having a cystic disease. The methods include the step of administering to the patient (a) an effective amount of one or more TMEM16a inhibitors; and (b) an effective amount of one or more lysophosphatidic acid antagonists, or an effective amount of one or more PPAR gamma agonists, or a combination thereof.
In another embodiment, described herein are methods for reducing cyst growth in a patient having or suspected of having a cystic disease. The methods include the step of administering to the patient (a) an effective amount of one or more TMEM16a inhibitors; and (b) an effective amount of one or more lysophosphatidic acid antagonists, or an effective amount of one or more PPAR gamma agonists, or a combination thereof.